Upconversion luminescence and temperature sensing characteristics of MgAl2O4 spinel doped with Er3+ and Yb3+ ions

Nanorod-shaped MgAl2O4: xEr3+, 0.05Yb3+ (where x ranges from 0.003 to 0.015) were synthesized using a low-temperature hydrothermal method. This study investigates the microstructure, upconversion luminescence performance, and temperature sensing characteristics of these phosphors. Results indicate that with increasing Er3+ doping, lattice distortions due to vacancy defects and lattice expansion first increase and then decrease, peaking at an Er3+ doping concentration of 0.015. A calcination temperature of 1100 degrees C was determined to be economically optimal, with a total weight loss of 38.5% during the precursor calcination process. Under 980 nm excitation, the intensity and ratio of red to green emissions peaked at an Er3+ doping concentration of 0.01. By controlling the doping level of Er3+ and the pump current of the excitation light, the chromatic transition from yellow to green and color purity can be finely tuned. The maximum temperature sensitivity (Samax) based on thermally coupled levels for Er3+ in MgAl2O4 is 40.28 x 10- 4 K- 1, and based on non-thermally coupled levels, Samax is 143.65 x 10- 4 K- 1, showing better performance than some common upconversion materials. Moreover, the calculated thermal activation energies for green and red transitions are Delta E545 = 0.4863 eV and Delta E658 = 0.4203 eV, respectively. The high temperature sensitivity and thermal activation energies suggest that these phosphors are promising candidates for non-contact temperature sensing applications.